Power consumption by computer peripheral devices, such as printers, display monitors, mass storage devices, and the like has become, with the expansion of computer installations, a significant portion of residential and commercial power requirements. For example, a typical color display monitor may consume as much as 50 to 80 percent of the total electrical energy consumed by a personal computer (PC). A display monitor dissipates this energy as visible light emissions from screen phosphors, thermal waste, electromagnetic radiation, high-energy radiation and acoustic energy. Only the phosphor emissions are normally considered useful and then only when actively being watched by an observer. The radiation emissions have been a hotly debated source of concern regarding possible health risks from long-term exposure. Manufacturers incur considerable extra expense to reduce radiation emissions from display monitors. Some people are annoyed by the acoustic emissions produced by some monitors. Thermal losses from display monitors contribute an additional load on air conditioning equipment. The energy efficiency of display monitors has historically improved mostly as a result of advances in the electronic circuit components such as the increased use of integrated circuit (IC) devices. Cathode ray tube (CRT) technology has improved rather little in terms of energy efficiency.
The number of PC's in regular use is growing rapidly and has reached a point where they have become major consumers of electric power. The United States Environmental Protection Agency has issued power efficiency targets for computer manufacturers to design for in new systems. Low-voltage IC's use less energy, and microprocessor power management techniques allow a computer to reduce energy consumption when idling. Until a suitable replacement for the CRT or a more efficient CRT is developed it will be difficult to substantially improve personal computer energy efficiency.
As described above, display monitors are not the only computer peripheral devices which consume large amounts of energy in use. Laser printers are another example. Other peripherals, such as mass storage devices, also consume electrical energy when not in full use, but to a lessed extent than do devices that have electrical heaters. In a typical working environment, printers are left on all the time as a convenience to users and are consequently consuming power in order to keep the fuser-heater at the proper operating temperature and the printer ready to print in response to instructions from a connected computer, i.e. a print request. A print request sent by a computer is received by the printer buffer and scheduled for printing, which typically commences when the buffer contains a full page and a "not busy" message is received from the printer. The fuser-heater is the principal consumer of power in a laser-type printer and typically a fan for dissipating heat from the fuser-heater is the main source of noise. If a printer is allowed to run continually and no printing instructions are received, the fuser-heater will be kept at a certain set temperature, the fan will continue to operate to cool the rest of the printer, and the printer will be in a ready state. If the printer is turned off when not being used, it will require a certain amount of time to bring the fuser-heater up to a proper temperature and begin carrying out instructions from the computer when it is turned on again in response to a print command. The amount of time required for a fuser-heater to reach operating temperature is dependent on several factors that are unique to each printer. The wait that is necessarily involved is awkward and costly in a multi-user environment.
With several computers and one or more printers running in an enclosed area, there may be a heat build-up that must be eliminated through climate control equipment to maintain a successful operation. If the principle heat-producing element in a laser-type printer, the fuser-heater, could be turned off for times of non-use, this problem would be considerably reduced.
What is needed is a way to shut down high-energy-consuming circuits in the display monitor, printers such as laser printers having fuser heaters, and in other peripheral devices, when the computer determines that full power on one or more of the connected peripheral devices isn't needed. This might be determined by a period of inactivity on input devices such a modem, mouse and keyboard, inactivity of peripheral devices, monitoring of a computer's internal bus, and in other ways, such as by a user-initiated input; for example an assigned "hot-key" input. Many computers and display terminals use such a technique to activate a screen blanking circuit or a program that displays moving images (or no image) to avoid burning the screen phosphors. Activating an input device such as pressing a key or moving a mouse causes the previous screen image to be restored. This technique can be extended to reduce peripheral device power consumption by signaling a microcontroller in a peripheral device, such as a monitor or printer, or an add-on device for "dumb" peripherals, to shut down or restore some or all of the device's electrical power circuits. One key to accomplishing this end is a means of signaling a monitor to shut down to some selected level without adding to the signals presently provided to a monitor.